Subject: [Dime] ABNF

From: Sarkar Biplab <[email-masked]>
Date: Mon, 25 Aug 2008 11:11:05 +0530

Hi All,

I would suggest some enhancements to the ABNF representation of the
diameter messages to indicate the "Mandatory Exclusion" of certain AVPs
in some messages.
The following type of information should be captured in the messages
description ABNF. (Say by using negative "max" count ).

======== RFC-3588 [6.2] ===================
   -  The Destination-Host and Destination-Realm AVPs MUST NOT be
      present in the answer message.

  ==================================

Any comments..

Thanks & Regards,
Biplab
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---

From: "Tschofenig, Hannes (NSN - FI/Espoo)" <[email-masked]>
Date: Mon, 25 Aug 2008 09:32:17 +0300

Hi Biplab, 
 
In some sense we should focus on the stuff that has to be present in the
message since with the Diameter extensibility mechanisms you cannot
really tell ahead of time what other AVPs will be present in the future
anyway. Hence, as a protocol designer you can really only work with the
following two things: 

* required AVPs (in the ABNF) as information that is important for the
sender to include

* mandatory AVPs (the stuff with the M-bit) as information that is
important for the receiver to understand. 

The mentioned case (pointing to Section 6.2) is, however, an interesting
one since this is a rather generic statement about Diameter message
processing since otherwise I would have said that one should reflect
these aspects in the ABNF by defining new commands. 

In some sense you are asking for a more formal way to describe things
that are currently presented in the text of the specification itself
rather than in the ABNF. ABNF isn't all that great when it comes to
conditional features (unless you define all sorts of new commands for
every stuff, which isn't really practical or readable either).

If we introduce new formalism into the ABNF itself then we run into a
lot of problems with backward compatibilty since there are a lot of
Diameter specifications out there already. Protocol designers extending
Diameter could, however, experiment with better ways to capture the
functionality of a specification. Maybe there are ways to capture
conditional behavior a bit better; for example by using pseudocode.

Ciao
Hannes

________________________________

	From: [email-masked] [mailto:[email-masked]] On
Behalf Of ext Sarkar Biplab
	Sent: 25 August, 2008 08:41
	To: dime
	Subject: [Dime] ABNF

		
	Hi All,
	
	I would suggest some enhancements to the ABNF representation of
the diameter messages to indicate the "Mandatory Exclusion" of certain
AVPs in some messages.
	The following type of information should be captured in the
messages description ABNF. (Say by using negative "max" count ).
	
	======== RFC-3588 [6.2] ===================
	   -  The Destination-Host and Destination-Realm AVPs MUST NOT
be
	      present in the answer message.

	Any comments..
	
	Thanks & Regards,
	Biplab